1. Technical Field
The present invention relates to a shaft rotary type linear motor and a shaft rotary type linear motor unit, which enable a driven object to rotate and linearly move.
2. Description of Related Art
Linear motors that operate by means of electromagnetic induction have compact bodies and can make fast movements, in comparison with mechanical actuators that operate, for example, with ball screw mechanisms. For example, many chip mounters (electronic component mounting devices) in semiconductor manufacturing apparatuses are equipped with rod-type linear motors. A rod-type linear motor includes a rod that has permanent magnets and coils that surround the rod. Further, it produces a thrust for the rod in its axial direction, on the basis of electromagnetic induction caused by a magnetic field created by the permanent magnets and current flowing through the coils, thereby linearly moving the rod.
Recently, a large number of techniques for improving a joint mechanism provided with a ball spline and a bearing, which couples a torque generator for a rotary motor to a thrust generator in a linear motor, have been proposed in order to cause linear motors to perform both rotational and linear moving operations.
One example of disclosed techniques associated with linear motors that can perform rotational and linear moving operations is an actuator with two degrees of freedom (see Japanese Patent No. 3300465). This actuator includes a rotary shaft that has a linear shaft and a spline groove in part of its circumference, and a spline guide bearing that engages with the spline groove.
Another example is a linear actuator that has a second shaft member disposed parallel to a rod of a linear motor (see Japanese Unexamined Patent Application Publication No. 2010-57357). In this linear actuator, the ends of the rod and the second shaft member are coupled to each other through a first joint member, so that the second shaft member linearly moves in relation to the linear movement of the rod. The second joint member couples the second shaft member to a housing in such a way that the second shaft member can linearly move but cannot rotate around the axis of the rod.